Well, so far, Chansey. It was the hardest Pokemon that I accually caught. But for other ones that are hard and still haven't caught are: Toroas, Kangaskhan, Scyther, and Shuckle.
After I found out that you can find Shiny Pokemon in the Safari Zone, I rarely go in any more. But they got alot of money from me in Emerald. Plus I caught so many Pikachu and Oddish. I don't even know why.
Remind me to remind me three days from yesterday to remind me about the thing I asked you to remind me of two days ago.